Means to reduce starting torque requirements for large centrifugal compressors



Aug. 19, 1969 E. B. ANDERSEN 3. 5

MEANS TO REDUCE STARTING TORQUE REQUIREMENTS FOR LARGE CENTRIFUGAL COMPRESSORS Filed Jan. 4, 1968 ERIK B. ANDERSEN United States Patent MEANS TO REDUCE STARTING TORQUE RE- QUIREMENTS FOR LARGE CENTRIFUGAL COMPRESSORS Erik B. Andersen, Maplewood, N.J., assignor to Worthington Corporation, Harrison, N.J., a corporation of Delaware Filed Jan. 4, 1968, Ser. No. 695,714 Int. Cl. Fb 1/10, 41/00, /00

US. Cl. 62-510 7 Claims ABSTRACT OF THE DISCLOSURE A centrifugal compressor refrigeration system having a small auxiliary reciprocating compressor which is connected to transfer refrigerant between the refrigeration system and a refrigerant storage container and also connected to evacuate the main centrifugal compressor prior to start-up of the system so as to reduce the torque necessary to bring the centrifugal compressor up to operating speed.

Background of the invention This invention relates to centrifugal compressor refrigeration systems and particularly to devices for unloading the centrifugal compressor during start-up.

Large centrifugal compressor refrigeration systems have extemely high torque requirements during start-up due to the fact that the cornpessor is doing work on the fluid being handled as the compressor is accelerated. In prior systems this required either a prime mover with an extremely high starting torque or else a large clutch for disengaging the compressor from the prime mover during start-up of the prime mover. If the prime mover is a gas turbine engine, high starting torques are simply not available and the expensive clutch would have to be utilized. If the prime mover is an electric synchronous motor, the need for the clutch could be eliminated by purchasing a motor having a high starting torque characteristic. However, for large size synchronous motors the cost of a motor having this high starting torque characteristic, commonly known as high pull-in torque can be as much as 20% greater than the cost of the same size motor With low pull-in torque.

Summary of the invention Accordingly, it is an object of this invention to provide a system for unloading a centrifugal compressor in a refrigeration system during the start-up system so as to reduce the starting torque required.

It is another object of this invention to provide a simple, less costly centrifugal compressor refrigeration system which can be easily started.

It is another object of this invention to eliminate the need for a clutch in a high speed gas turbine driven centrifugal compressor refrigeration system.

These objects are met by utilizing the small reciprocating pump out compressor, which is normally in the system to transfer refrigerant from the system to a storage tank, for evacuating the compressor unit during start-up so as to reduce the torque required to bring the compressor up to speed.

Drawings FIGURE 1 is a diagrammatic view of a refrigeration system embodying this invention.

Description Referring to the diagram, the refrigeration system shown therein comprises in general an evaporator 2, a main refrigerant condenser 4 for liquifying and dellvering low pressure liquid refrigerant to the evaporator 2 after passing through a flash chamber 6. A rotary twostage centrifugal compressor 8 has a suction line 10 connected to the evaporator and a discharge line 12 connected to the condenser. The centrifugal compressor is driven by a gas turbine engine 14, although other prime movers, such as a synchronous motor, could also be utilized to drive the compressor.

An auxiliary system including a small reciprocating compressor 16, an auxiliary condenser 18, a refrigerant storage tank 20 and suitable piping and valves is connected into the main refrigeration system by lines 22 and 24. A valve system generally indicated by numeral 26 and including valves 28, 30, 32, and 34 is designed to connect the reciprocating compressor for pumping refrigerant in either direction between the main system and the refrigerant storage tank 20.

Refrigerant which vaporizes in the flash chamber 6 is drawn into the second stage of the compressor via line 40. The inlet lines 10 and 40 to the compressor contain valves 42 and 44, respectively for blocking flow of refrigerant into the compressor while the refrigerant discharge line 12, includes a check valve 46. The discharge side of the small reciprocating compressor is connected to the valve system by line 54, while the suction can be connected to the valve system, via lines 48 and 50, or to the main compressor via lines 22 and 50. Lines 56 and 24 interconnect the refrigerant storage tank 20, and the top of the condenser 4, respectively with opposite sides of the valve system between the compressor suction and discharge connections of the valve manifold. The operation of this valve system is described in detail below.

The main condenser 4 is provided with an internal coil 60 through which cooling medium is circulated to condense the compressed refrigerant gas received from the main compressor via line 12. The evaporator 2 is also provided with an internal coil 62 through which evaporating medium may be circulated to vaporize the liquid refrigerant admitted to the evaporator so as to cool the evaporating medium.

The various elements of the main refrigeration system are old and well known in the art, as is the use of a small reciprocating compressor for pumping refrigerant to a. refrigerant storage tank during prolonged shut down of the system; but the use of the reciprocating compressor to unload the main compressor constitutes an important feature of this invention.

.During normal operation of the refrigeration system a conventional refrigeration loop is formed between the compressor 8, condenser 4, flash chamber 6 and the evaporator 2 with valves 42 and 44 being opened and valves 30, 32 and 52 being closed. When it is desirable to withdraw all of the refrigerant from the system and place it in the storage tank 20 the compressor 16 is turned on and valves 30 and 34 are opened so that refrigerant will be drawn from the top of the condenser for forwarding to the storage tank via lines 12, 24-, 68, '70, 48, 54, 72, 74 and 56 until all of the refrigerant is in the refrigerant storage tank. T0 recharge the system with refrigerant from the storage tank, valves 28 and 32 are opened while valves '30, 34 and 52 remain closed. The small reciprocating compressor is then used to pump refrigerant back into the system via lines 56, 76, 48, 54, 78 and 12.

Prior to start-up of the gas turbine and compressor, which is connected to the turbine by shaft 80, valves 42 and 44 are closed to block the fiow of refrigerant into the compressor and valves 52 and 32 are open. Valves 28, 30 and 34 remain closed. By operating the small reciprocating compressor, the main compressor can be evacuated and the refrigerant discharged into the condenser via lines 22, 50, 54, 78, 24 and 12. With the compressor evacuated,

the gas torque necessary to bring the compressor up to speed will be essentially zero and the only contribution of the compressor to the overall start-up torque requirements will be the torque necessary to accelerate the inertia of the compressor rotor to the rated speed within a reasonable time. After the compressor is brought up to operating speed valves 42 and 44 are opened to begin normal operation of the refrigeration system.

What is claimed is:

1. A refrigeration system comprising:

(a) a centrifugal compressor, a condenser, expansion means and an evaporator serially connected to form a refrigeration loop;

(b) a storage tank capable of receiving the entire refrigerant charge in the system;

(c) an auxiliary compressor;

(d) means for connecting the auxiliary compressor between the storage tank and the refrigerant loop for either supplying refrigerant to, or removing refrigerant from the system;

(e) valves in the system for isolating the centrifugal compressor; and

(f) means for connecting the auxiliary compressor between the centrifugal compressor and the condenser; whereby the centrifugal compressor can be evacuated prior to start-up of the system to reduce the torque necessary to bring the compressor up to speed by closing the valves which isolate the main compressor and connecting the auxiliary compressor between the centrifugal compressor and the condenser.

2. The refrigeration system defined in claim 1 wherein, the valves for isolating the centrifugal compressor include a first valve between the evaporator outlet and the main compressor inlet and a check valve betwen the centrifugal compressor outlet and the condenser inlet.

3. The system defined in claim 1 wherein, the centrifugal compressor includes two stages of compression, the expansion means includes a flash chamber which is connected to the centrifugal compressor at the second stage suction and a valve is located betwen the flash chamber and the second stage suction.

4. The system defined in claim 2 wherein, the centrifugal compressor includes two stages of compression, the expansion means includes a flash chamber which is connected to the centrifugal compressor at the second stage suction and a valve is located between the flash chamber and the second stage suction.

5. A refrigeration system comprising:

(a) a multiple stage centrifugal compressor;

(b) a condenser;

(c) a discharge conduit connecting the centrifugal compressor and the condenser;

(d) an evaporator;

(e) a conduit connecting the condenser and the evaporator and having a flash chamber therein;

(f) a first suction conduit connecting the evaporator and the first stage of the centrifugal compressor;

(g) a second suction conduit connecting the top of the flash chamber and an intermediate stage of the centrifugal compressor;

(h) a valve in each of the suction conduits and in the discharge conduit;

(i) an auxiliary compressor; and

(j) means for connecting the auxiliary compressor between the centrifugal compressor and the condenser for evacuating the centrifugal compressor prior to start-up of the system.

6. The system defined in claim 5, wherein, the valves in the suction conduits are shut-off valves and the valve in the discharge conduit is a check valve for preventing flow from the condenser to the compressor.

7. A refrigeration system having a centrifugal compressor, a condenser an expansion valve and an evaporator serially connected to form a refrigeration loop and a pump out compressor for transferring refrigerant between the refrigerator loop and a storage tank wherein the improvement comprises valve means for isolating the centrifugal compressor and means for connecting the pump out compressor between the centrifugal compressor and the remainder of the refrigeration loop whereby it will be possible to evacuate the centrifugal compressor prior to start-up so as to reduce the torque necessary to rotate the centrifugal compressor.

References Cited UNITED STATES PATENTS MEYER PERLIN, Primary Examiner U.S. C1. X.R. 

